1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an in-plane switching (IPS) mode LCD capable of preventing signal interference of a data line and reducing a vertical line deficiency.
2. Discussion of the Related Art
Recently, as various mobile electronic devices including a mobile phone, a PDA or a notebook computer are being developed, demands for a light, thin, short and small flat panel display device which may be applied to the mobile electronic devices are increasing. Thus, researches for flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and a vacuum fluorescent display (VFD) are actively ongoing. Among these display devices, the LCD is most spotlighted because it provides easy mass-production, easiness of a driving unit, and high picture quality.
In general, an LCD device implements an image by controlling light by using an electric field, including a liquid crystal panel on which pixels are arranged in a matrix form and a driving circuit for driving the liquid crystal panel.
FIG. 1 illustrates a unit pixel region of the related art IPS mode LCD. As shown in FIG. 1, a gate line 1 and a data line 10 are arranged to cross each other to define pixel regions on a first substrate of the liquid crystal panel. A gate electrode 9, a semiconductor layer (not shown) and source/drain electrodes 13 and 15 are formed at the crossing of the gate line 1 and the data line 10, thereby forming a switching device of a thin film transistor TFT.
A pixel electrode 3 and a common electrode 5 are alternately disposed at each pixel region of the liquid crystal panel to generate an in-plane electric field (i.e., horizontal electric field) on the first substrate. The pixel electrode 3 receives a data signal from the source/drain electrodes 13 and 15 of the switching device TFT and generates the in-plane electric field with the common electrode 5 on the first substrate.
In other words, the gate electrode 9 and the source/drain electrodes 13 and 15 are connected with the gate line 1 and the data line 10, respectively, to turn on the switching device TFT with a signal inputted through the gate line 1 and to transfer a data signal applied through the data line 10 to the pixel electrode 3. As a result, the LCD displays an image by controlling the light transmittance of liquid crystal molecules with the in-plane electric field formed between the pixel electrode 3 and the common electrode 5 according to the data signal supplied to each pixel region.
Although not shown in the drawing, a color filter layer is formed on a second substrate, and a liquid crystal layer is formed at a space between the first and second substrates. In such an IPS mode LCD, liquid crystal molecules of the liquid crystal layer are driven by the in-plane electric field formed between the pixel electrode and the common electrode. As such, a visible range widens compared to the conventional twisted nematic (TN) mode LCD, namely, obtaining a viewing angle of about 80°˜85° in all directions (i.e., up/down and left/right directions).
However, in the conventional IPS mode LCD, the data line 10 and the pixel electrode 3 are adjacently disposed in parallel. Thus, a signal interference can be easily generated between the data line 10 and the pixel electrode 3, thereby causing a cross-talk and a light leakage phenomenon.
Accordingly, in an effort to solve such a problem, an outermost common electrode 5′ is disposed near the data line 10 and has a width greater than the other common electrode 5. However, such an electrode disposition structure degrades an aperture ratio of the LCD and distorts of the electric field because a signal interference of the data line cannot be effectively prevented.
FIGS. 2A and 2B are enlarged views of the region ‘I’ shown in FIG. 1. With reference to FIGS. 2A and 2B, a distortion of the liquid crystal array due to a signal interference according to a voltage variation of the data line will be described in detail.
A rubbing direction inducing an initial arrangement of liquid crystal molecules has about 45° tilt to the common electrodes 5 and 5′ and the pixel electrode 3, and an in-plane electric field generated, when a voltage is applied to the common electrodes 5 and 5′ and the pixel electrode 3, is perpendicular to the common electrodes 5 and 5′ and the pixel electrode 3.
FIG. 2A shows that when a voltage of 8V is applied to the data line 10 and voltages of 5V and 8V are respectively applied to the common electrodes 5 and 5′ and the pixel electrode 3, a director of the liquid crystal molecules is determined as a first direction 30 by the in-plane electric field generated due to a voltage difference between the common electrodes 5 and 5′ and the pixel electrode 3.
In FIG. 2B, a voltage of 8V is applied to the data line 10 and voltages of 5V and 8V are applied respectively to the common electrodes 5 and 5′ and the pixel electrode 3. If the 8V applied to the data line 10 is changed to 10V, a direction of the electric field generated on the actual driving region of the liquid crystal molecules is changed. As a result, a second direction 35 is rotated more than the first direction 30 shown in FIG. 2A.
A voltage change of the data line distorts the direction of the electric field in the pixel region, thereby causing a change in the arrangement of liquid crystal molecules. Therefore, even if the same voltage is applied to the common electrodes and the pixel electrode, color sense can be changed on a display screen.